Threshold and Observers

Question 1

ophthalmologist. One of the first to figure out that our physiology is providing us our sensations.

Answer 1

Helmholtz

Question 2

Threshold

Answer 2

The minimum quantity of a stimulus that can be detected.

Question 3

Examples of visual thresholds

Answer 3

VAs
Motion detection- what is the slowest motion someone can recognize?
Depth
Color differences
Detection of flicker
Orientation differences- is something vertical, or at an angle?

Question 4

Absolute threshold

Answer 4

Minimum stimulus strength needed to reliably detect the presence vs the absence of the stimulus. Is it there or not?

Question 5

Difference threshold

Answer 5

Minimum change in stimulus strength needed to reliably detect the difference between two stimulus. What is the difference between the two?

Question 6

Perfect observers

Answer 6

Would give same threshold each time measured.

For all intensity values below the threshold magnitude, the observer will never say the stimulus is present. For all intensity values at or above threshold, the observer will always say the stimulus is present.

Humans are not perfect observers.

Question 7

Real observer

Answer 7

Measured threshold varies.
Represented by the psychometric function, AKA frequency of seeing curve.

As the stimulus intensity is increased, the probability that the observer will detect the stimulus increases.

For absolute threshold tasks (is it there or not?), the threshold is that stimulus magnitude for which the observer can correctly detect its presence on 50% of the trials.